The changes of membrane lipids in apple (Malus domestics Borkh. cv. Delicious) auxillary and terminal buds from August to April were determined. The predominant lipids were monogalactosyl diglyceride (MGDG), digalactosyl diglyceride (DGDG), phosphatidylcholine (PC), and phosphatidylethanolamine (PE). An increase in membrane polar lipids was associated with budbreak and bud growth from August to April. Linolenic acid was the predominant fatty acid in MGDG, DGDG, and PC, while linoleic acid was predominant in PE. Phosphatidylglycerol (PG) and phosphatidylinositol (PI) contained a high amount of palmitic acid. The ratio of (18:2 + 18:3) to 18:1 fatty acids in galactolipids in apple buds increased from August to April. ß-Sitosterol and sitosteryl ester were the predominant sterols in apple buds. An increase in sitosterol, a decrease in sitosteryl ester, and a decline in the ratio of free sterols to phospholipids occurred during budbreak in spring. A decrease in sitosterol was associated with bud expansion in spring.
Shiow Y. Wang and Miklos Faust
Charles W. Heuser and Charles E. Hess
Three lipid-like root-promoting compounds were isolated from the easy-to-root juvenile form of English ivy, Hedera helix L. The purification procedure involves extracting with methanol-chloroform and chromatography on columns of charcoal-celite, silica gel and LH-20 Sephadex. Ultraviolet and infrared spectroscopic studies suggest the presence of alcohol and nitrile functional groups. The 3 compounds are unstable and the instability is greatest when the substances are purified. In the purified state, the lipid-like compounds are colorless but become orange-yellow after breakdown. A loss of root-promoting activity occurs with the color change.
T.G. McCollum, R.E. McDonald, and H.E. Nordby
The objective of this work was to determine if lipid composition of grape fruit flavedo tissue differed with canopy position and if changes in flavedo lipid composition occurred during the development of chilling injury (CI). `Marsh grapefruit were harvested from interior (IN) and exterior (EX) canopy positions and stored at 5C for up to 8 weeks. During storage, EX fruit developed severe CI, whereas IN fruit developed only trace CI. Electrolyte leakage from EX fruit flavedo increased during storage and significantly greater than from IN fruit At the time of harvest, flavedo oleate and linoleate, on a μg % basis, were higher in IN than in EX fruit During storage at 5C, the amount of oleate in IN fruit flavedo decreased and was similar to EX fruit after 4 weeks at 5C. The relative amount of flavedo linoleate decreased in IN fruit and increased in EX fruit during storage at 5C and following 8 weeks at 5C was higher in EX fruit than in IN fruit At the time of harvest, total lipid P in flavedo was higher in IN fruit than in EX fruit; during storage the amount of flavedo lipid P in IN fruit decreased and was equivalent to EX fruit following 8 weeks at 5C. Total sterols in flavedo did not differ with canopy position and remained constant during storage.
Loreto R. Pascual and Robert C. Wiley
Seven mutant maize genotypes with sweet corn backgrounds and 4 commercially grown sweet com cultivars were harvested from 18-45 days after pollination (DAP). The lipids were extracted, separated into major lipid fractions, transesterified and measured as methyl esters of palmitic (16:0), stearic (18:0), oleic (18:1), linoleic (18:2) and linolenic (18:3) acids by gas liquid chromatography (GLC). Neutral lipids had a low ratio of polyunsaturates to monounsaturates (1.7:1), i.e., linoleic and linolenic to oleic fatty acids. Glycolipids had the highest proportion of linoleic and linolenic acids. Phospholipids tended to be more saturated than other fractions because of their high proportion of palmitic acid. All fatty acids in the neutral lipid fraction increased on an absolute basis with advancing maturity. Fatty acids in the glycolipid and phospholipid fractions generally peaked at 28 DAP on a mg fatty acid/g corn wet weight basis and then decreased with increased maturity. The percentage of oleic acid in the glycolipid fraction doubled from 12-24 percent during the 18-45 DAP period. Experimental lines and commercial cultivars contained 18.4, 1.4, 21.5, 57.1 and 2.1 percent respectively of palmitic, stearic, oleic, linoleic and linolenic acid over the maturity ranges studied.
Harold E. Nordby, Steven Nagy, and John M. Smoot
Major leaf alkanes (C29-C33) of 2 scions on 10 rootstocks of citrus were examined by gas chromatography. A small but definite effect of the rootstock on the alkane profiles of the scions was observed. The effect of rootstock on alkane patterns in juice sacs was very small. Rootstock affected the fatty acid patterns of total and neutral lipids as well as of triglycerides and sterol esters.
Polyamines are effective scavengers of activated oxygen free radicals produced by lipoxygenase (LOX) and phospholipase-D (PL-D). Activated oxygen free radicals cause peroxidative damage to membranes and hasten senescence. Exogenous polyamine spermidine (SPD) compared to spermine (SPM) at 1 mM or no polyamine was an effective inhibitor of honey dew (Cucumis melo L. var. inodorus) membrane peroxidation, as determined by malondialdehyde (MDA), following dark incubation for 6 or 48 hours of fully abscised fruit hypodermal mesocarp tissue. MDA levels in SPD-treated tissue was lowest in both 6 and 48 hours compared to SPM or no polyamine. SPD was effective in slowing lipid peroxidation as MDA was highly negatively correlated with the loss in total chlorophyll, plasma membrane H+ pumping ATPase activity, and microsomal phospholipid content (r = -0.89, -0.64 and -0.57, respectively). Both LOX and PL-D enzyme activities were not correlated with the total chlorophyll and microsomal membrane phospholipid losses or MDA levels, demonstrating that these enzymes act indirectly in the degradation of membranes through the production of lipid peroxidating free radicals. The results also demonstrate that the effect of polyamines as anti-senescence compounds is through direct inhibition of lipid peroxidation and not by affecting LOX or PL-D free radicle production.
Bruce D. Whitaker
Lipid composition and pigment content were determined in pericarp of `Pik Red' tomatoes (Lycopersicon esculentum Mill.) that were harvested when mature-green (MG) then ripened for 1 or 14 days at 20C, chilled for 11 or 21 days at 2C, or chilled for 21 days and transferred to 20C for 4 days (rewarmed). During ripening, chlorophyll fell below a detectable level, carotenes increased 100-fold, phospholipids (PLs) dropped ≈20%, and galactolipids (GLs) dropped ≈35%. Fatty-acid unsaturation decreased slightly. Steryl esters (SEs), more than free sterols (FSs) and steryl glycosides (SGs), increased at the expense of acylated steryl glycosides (ASGs), and in all four steryl lipids, the stigmasterol: sitosterol ratio rose dramatically, whereas the level of isofucosterol fell sharply. During chilling, chlorophyll declined ≈40% and carotenes ≈60%. PL content did not change, whereas GL fell ≈15%. Fatty-acid unsaturation increased slightly. FS, much more than SG and SE, increased at the expense of ASG. The stigmasterol: sitosterol ratio changed little in ASG, SG, and SE but declined in FS. Isofucosterol increased in FS and SE. Rewarming had little effect on the levels of chlorophyll, carotenes, or PL levels, but caused GL to fall another ≈15%. Fatty-acid unsaturation decreased slightly in GL and ASG. The distribution of total sterol in ASG, SG, FS, and SE changed dramatically, yielding proportions close to those in unchilled MG fruit. Also, 4 days after rewarming, the stigmasterol: sitosterol ratio had increased sharply, particularly in FS and SE, and there was a further rise in isofucosterol in all four steryl lipids. These results indicate that chloroplast damage occurs during chilling, but PL-rich cell membranes are not degraded, even upon rewarming. Changes in sterol composition and conjugation during chilling and after rewarming could result in membrane dysfunction.
Durward Smith and Susan Cuppett
Both fresh and frozen asparagus rapidly deteriorate in quality due, in part, to the formation of oxidative off-flavors. Anti-oxidants and chelating agents prevent lipid oxidation in vegetables, but increasing the levels of such compounds in whole vegetables is difficult. Vacuum infusion was optimized to saturate asparagus spears with ascorbic acid without damaging tissues. The combination of vacuum infusion of ascorbic acid and thermal blanching effectively prevented the formation of oxidative off-flavors and hexanal during frozen storage. Sensory evaluations correlated with hexanal levels following frozen storage.
Eric A. Curry
solvent-extractable lipid extraction and analysis. Fruit treated at harvest were rated for injury 1 month after treatment, after which two fruit from each treatment replication were selected for epicuticular wax analysis. From an area of the peel visually
Bruce D. Whitaker
MG tomato fruit were stored for four or 12 days at chilling (2C) or nonchilling (15C) temperature. Fruits stored 12 days at 15C ripened to the turning stage, whereas fruits at 2C did not ripen. Lipids of microsomes and plastids from pericarp tissue were analyzed at harvest and after four or 12 days of storage. After 12 days at either 15C or 2C, the ratio of phospholipid (PL) to protein in microsomes declined, with a concomitant increase in the ratio of total membrane sterols (TMS) to PL. The TMS/PL ratio also increased in crude plastids. In both microsomes and plastids, free sterols (FS) increased more at 2C than at 15C, and thus accounted for a larger percentage of the TMS. The ratio of stigmasterol to sitosterol in steryl lipids, particularly in FS, increased more at 15C than at 2C. The unsaturation index of fatty acids in PL and galactolipids generally increased slightly during storage at both 15C and 2C. The ratio of phosphatidylethanolamine to P-choline increased in both membrane fractions at both temperatures. In plastids, the ratio of mono- to digalactosyldiacylglycerol declined substantially at 2C but not at 15C.